#!/bin/bash

cat <<'EOF'

For a demo, try running this script as follows:

  snippet-special-params a b c "one two three" d " " e ' f
   g' h 'i j'

EOF


#------------------------------------------------------------------------------
# Provide `echoargs`, a way to print an array for testing purposes.
#------------------------------------------------------------------------------

echoargs()
{
  # see http://stackoverflow.com/questions/6723426/looping-over-arrays-printing-both-index-and-value 
  #   ... you would find the array keys with "${!foo[@]}" ... 
  args=("$@")
  for i in "${!args[@]}"; do
    echo "\$$i=${args[$i]}"
  done
}


cat <<'EOF'

  $* Expands to the positional parameters, starting from one. When the
expansion is not within double quotes, each positional parameter
expands to a separate word. In contexts where it is performed, those
words are subject to further word splitting and pathname expansion.
When the expansion occurs within double quotes, it expands to a single
word with the value of each parameter separated by the first character
of the IFS special variable. That is, "$*" is equivalent to "$1c$2c…",
where c is the first character of the value of the IFS variable. If
IFS is unset, the parameters are separated by spaces. If IFS is null,
the parameters are joined without intervening separators.

$* is:
EOF
echoargs $*
cat <<'EOF'

"$*" is:
EOF
echoargs "$*"
cat <<'EOF'

  $@ Expands to the positional parameters, starting from one. When the
expansion occurs within double quotes, each parameter expands to a
separate word. That is, "$@" is equivalent to "$1" "$2" …. If the
double-quoted expansion occurs within a word, the expansion of the
first parameter is joined with the beginning part of the original
word, and the expansion of the last parameter is joined with the last
part of the original word. When there are no positional parameters,
"$@" and $@ expand to nothing (i.e., they are removed).

$@ is:
EOF
echoargs $@
cat <<'EOF'

"$@" is:
EOF
echoargs "$@"
cat <<'EOF'

  $# Expands to the number of positional parameters in decimal.
EOF
cat <<EOF

\$# is ($#)
EOF
cat <<'EOF'

  $? Expands to the exit status of the most recently executed
foreground pipeline.
EOF
cat <<EOF

\$? is ($?)
EOF
cat <<'EOF'

  $-, a hyphen. Expands to the current option flags as specified
upon invocation, by the set builtin command, or those set by the
shell itself (such as the -i option).
EOF
cat <<EOF

\$- is ($-)
EOF
cat <<'EOF'

  $$ Expands to the process ID of the shell. In a () subshell, it
expands to the process ID of the invoking shell, not the subshell.
EOF
cat <<EOF

\$$ is ($$)
EOF
cat <<'EOF'

  $! Expands to the process ID of the job most recently placed into
the background, whether executed as an asynchronous command or using
the bg builtin (see Job Control Builtins).
EOF
cat <<EOF

\$! is ($!)
EOF
cat <<'EOF'

  $0 Expands to the name of the shell or shell script. This is set at
shell initialization. If Bash is invoked with a file of commands (see
Shell Scripts), $0 is set to the name of that file. If Bash is started
with the -c option (see Invoking Bash), then $0 is set to the first
argument after the string to be executed, if one is present.
Otherwise, it is set to the filename used to invoke Bash, as given by
argument zero.
EOF
cat <<EOF

\$0 is ($0)
EOF
cat <<'EOF'

  $_, an underscore. At shell startup, set to the absolute pathname
used to invoke the shell or shell script being executed as passed in
the environment or argument list. Subsequently, expands to the last
argument to the previous command, after expansion. Also set to the
full pathname used to invoke each command executed and placed in the
environment exported to that command. When checking mail, this
parameter holds the name of the mail file.
EOF
cat <<EOF

\$_ is ($_)

EOF

